It was needed on macOS for a time when BUrl used regexes for parsing.
Now it does not, and so we can remove libshared's RegExp from build
libshared, and thus also libgnuregex.
PowerPC was special-cased to not include posix/regex.h but a local copy.
This caused a warning for undefining __STDC__ and a pointer signedness error.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@38257 a95241bf-73f2-0310-859d-f6bbb57e9c96
